00:01
So we want to know the conditional probability that exactly four heads appear when a fair coin is flipped five times, given that the first flip, first flip is a head.
00:24
Well, let e be the event that exactly four heads appear.
00:32
Four heads.
00:34
Let f be the event that the first flip comes up heads.
00:43
Heads.
00:46
Well, we know that the probability of f is equal to 2 to the fourth power over 2 to the 5th.
01:02
2 to the 5th.
01:03
And that is because there are 2 to the 5th possible outcomes, since we're flipping 5 times and we can have either heads or tails for each outcome.
01:13
And for the 1st, for the 2 to the 4th, it is because we know that the first outcome is a head, and then for the fourth other outcomes, we can either have heads or tails.
01:26
And this is equal to one half.
01:29
So the probability that the first flip is ahead is one half.
01:36
Now, for the probability of.....